Brake pressure control device

Abstract

A hydraulic twin-circuit brake system for a road vehicle with front axle/rear axle brake circuit division, is equipped both with an anti-lock brake system (ABS) and an acceleration skid regulation device (ASR) which operates on the principle of slowing down a driven vehicle wheel tending to spin by activating its wheel brake. A brake pressure control device analogous to the acceleration skid regulation device is also provided for the brake circuit of the non-driven front wheels of the vehicle. This brake pressure control device, together with the acceleration skid regulation device for the driven rear wheels of the vehicle, is activated in the sense of an automatic brake pressure control when the driver actuates the brake pedal at a rate which is larger than a specified threshold value φ s . The brake pressure is then automatically controlled such that optimum vehicle deceleration occurs. Buffer reservoirs which are connected to the outlet pressure spaces of the brake unit, instead of to the wheel brakes, during automatic braking achieve a pedal displacement simulation by way of which an electronic control unit recognizes the vehicle deceleration which the driver wishes to select by the brake pedal actuation.

We claim: 
     
       1. A brake pressure control device for a road vehicle having a pedal-actuated brake unit, a hydraulic multi-circuit brake system with static brake circuits, into which brake system pressures proportional to a pedal force can be connected by actuation of the brake unit, and an anti-lock brake system configured for dynamically stable deceleration behavior of the road vehicle and having a sensor device operationally arranged for recording the position of one of a brake pedal and of a brake unit element connected to the motion of the brake pedal and generating electrical output signals characteristic of the instantaneous position of the brake pedal, an electronic control unit for processing the output signals and generating control signals for an electrically controllable brake pressure setting device so that at least a higher brake pressure than an expected brake pressure value associated with the instantaneous pedal position is connected with front wheel brakes at least whenever the speed with which a position of a pedal changes during a brake pressure build-up actuation is greater than a specified threshold value in excess of zero, and at least one buffer reservoir controllable, via an operatively associated respective valve, by output signals of the electronic control unit and configured to be pressurized against a lower return force than that corresponding to a reaction force resulting from a reaction of the brake pressure on the brake unit, wherein the at least one buffer reservoir is operatively arranged to be connected, by position selection of the valve by an output signal of the electronic control unit actuating the brake pressure control device to a pressure outlet of the brake unit which is associated with that brake circuit in which higher level brake pressure occurs, and an outlet pressure space of the brake unit connected to the at least one buffer reservoir is shut off, under valve control, from the brake circuit subjected to the increased brake pressure on actuation of the brake pressure control device. 
     
     
       2. The brake pressure control device according to claim 1, wherein the at least one buffer reservoir comprises a buffer reservoir provided for two vehicle brake circuits. 
     
     
       3. The brake pressure control device according to claim 1, wherein the at least one buffer reservoir is configured with a preloaded return spring and a reservoir piston. 
     
     
       4. The brake pressure control device according to claim 3, wherein that at least buffer reservoir is provided with a preloading device configured such that, when the brake pressure control device is not actuated, the preload of the return spring at a value which corresponds to that force which results from the reservoir piston being subjected to the outlet pressure of the connected outlet pressure space of the brake unit. 
     
     
       5. The brake pressure control device according to claim 4, wherein the preloaded return spring is operatively arranged between two pistons, one of which pistons forms an axially movable boundary of the reservoir chamber and the other of which pistons forms an axially movable boundary of a control pressure space into which a pressure corresponding to the pressure in the connected outlet pressure space of the brake unit is permanently connected when the brake pressure control device is not actuated. 
     
     
       6. The brake pressure control device according to claim 5, wherein a pressure follow-up in the control pressure space of the at least one buffer reservoir is effected by an operative connection, via a pulse-controlled follow-up valve, of one of the outlet pressure of the auxiliary pressure source and the control pressure space to the unpressurized storage reservoir of the auxiliary pressure source. 
     
     
       7. The brake pressure control device according to claim 6, wherein the follow-up valve is configured as a 3/3-way solenoid valve arranged to be driven by a first control signal with a first relatively low control current from its basic position, in which the control pressure space is connected to the storage reservoir of the auxiliary pressure source and is shut off from a high pressure outlet of the auxiliary pressure source, into a first excited, shut-off position in which the control pressure space is shut off from both the high pressure outlet of the auxiliary pressure source and its storage reservoir, and which can be driven by a second control signal current which is relatively higher than the first control current into a second excited position, in which the control pressure space of the at least one buffer reservoir is connected to the high pressure outlet of the auxiliary pressure source and is shut off from its storage reservoir. 
     
     
       8. The brake pressure control device according to claim 5, wherein a pressure sensor is operatively arranged for recording the pressure in the control pressure space of the at least one buffer reservoir, and a pressure sensor is operatively arranged for recording the pressure in the connected outlet pressure space of the brake unit. 
     
     
       9. The brake pressure control device according to claim 3, wherein the at least one buffer reservoir comprises a buffer reservoir provided for each of the two vehicle brake circuits. 
     
     
       10. The brake pressure control device according to claim 1, in which the vehicle has front axle/rear axle brake circuit division, wherein at least one pressure sensor is operatively arranged for generating an electrical output signal characteristic of the pressure in the outlet pressure space of the brake unit associated with the front axle brake circuit, and at least one pressure sensor is operatively arranged for generating an electrical output signal characteristic of the pressure in at least one of the front wheel brakes. 
     
     
       11. The brake pressure control device according to claim 1, wherein for each outlet pressure space of the brake unit, a pressure sensor is operatively arranged for generating an electrical output signal characteristic of the particular outlet pressure, and at least one pressure sensor is operatively associated with each of the brake circuits. 
     
     
       12. The brake pressure control device according to claim 1, wherein at least one pressure modulator constitutes a brake pressure setting element of the brake pressure control device, in which modulator a piston forms a movable pressure-tight boundary between a control pressure space such that, when the control pressure space and an outlet pressure space are subjected to the valve-controlled outlet pressure of an auxiliary pressure source, the piston is arranged to be displaced in a direction of a brake pressure build-up in the brake circuit connected to the outlet pressure space, and, via valve-controlled connection to a storage reservoir of the auxiliary pressure source, the piston is arranged to be displaced in a direction of a pressure reduction in the connected brake circuit the piston being pressed by a preloaded, spring-elastic return element into its basic position corresponding to minimum volume of the control pressure space and maximum volume of the outlet pressure space. 
     
     
       13. The brake pressure control device according to claim 12, wherein the at least one buffer reservoir comprises a buffer reservoir provided for the two vehicle brake circuits. 
     
     
       14. The brake pressure control device according to claim 12, wherein brake pressure control valves are operatively arranged for connecting the control pressure space of the at least one pressure modulator alternately to the high pressure outlet of the auxiliary pressure source and to its storage reservoir and are configured as 3/3-way solenoid valves, whose basic position is a flow position shutting off the control pressure space of the at least one pressure modulator from the high pressure outlet but connecting it to the storage reservoir of the auxiliary pressure source, whose first excited position, taken up on excitation of the control magnet by a first control signal of relatively low control current is a shut-off position in which the control pressure space is shut off from both the high pressure outlet of the auxiliary pressure source and its storage reservoir, and whose second excited position, taken up on excitation of their control magnet by a second control signal of relatively higher control current than the first control signal is again a flow position in which the control pressure space of the pressure modulator is connected to the high pressure outlet of the auxiliary pressure source but is shut off from its storage reservoir. 
     
     
       15. The brake pressure control device according to claim 1, wherein 3/3-way solenoid valves are operatively arranged as function control valves which effect the connection of the at least one buffer reservoir at the associated outlet pressure space of the brake unit, the basic position of the solenoid valves being a flow position shutting off the associated outlet pressure space of the brake unit from the reservoir chamber of the at least buffer reservoir but connecting the associated outlet pressure space to the continuing section of the main brake pipe of the related brake circuit, the 3/3-way solenoid valves, on excitation of their control magnet by a first control signal of relatively low current taking up a first excited, shut-off position in which the outlet pressure space of the brake unit is shut off both from the reservoir chamber of the at least one buffer reservoir and from the continuing main brake pipe section and, on excitation of their control magnet by a second control signal of relatively higher current than the first control signal taking up a second excited position, which is again a flow position, in which the outlet pressure space of the brake unit is connected to the reservoir chamber of the at least one buffer reservoir but is shut off from the continuing main brake pipe section. 
     
     
       16. The brake pressure control device according to claim 1, wherein the at least one buffer reservoir is connected, via a respective 2/2-way solenoid valve, to one of the pressure outlets of the brake unit, and the electrically controllable brake pressure setting device constituted as at least one pressure modulator having an outlet pressure space connected to a brake pipe section continuing to one of an anti-lock brake system and the wheel brakes of the particular brake circuit and a piston forming a movable pressure-tight boundary between the outlet pressure space and a control pressure space is connected to the pressure outlet of the brake unit via a valve whose basic position is a flow position connecting the pressure outlet of the brake unit, in the basic position of the modulator piston, to the outlet pressure space of the pressure modulator and which, controlled by displacement of the modulator piston, reaches its shut-off position after a small fraction of the pressure build-up stroke of the modulator piston and is brought back to its open position by a return of the modulator piston to its basic position. 
     
     
       17. The brake pressure control device according to claim 16, wherein the at least one buffer reservoir comprises a buffer reservoir provided for each of the two vehicle brake circuits. 
     
     
       18. The brake pressure control device according to claim 1, wherein the device is configured as an additional unit to one of a conventional vehicle brake system and a vehicle brake system equipped with an anti-lock brake system. 
     
     
       19. The brake pressure control device according to claim 1, wherein, in a road vehicle which is equipped with at least one of both an anti-lock brake system and a device for acceleration slip regulation of the driven wheels and a device for electronically controlled front axle/rear axle brake force distribution, means is operatively arranged for subjecting the brake circuit of the non-driven vehicle wheels to brake pressure control, as a function of the brake pedal position and its changes. 
     
     
       20. The brake pressure control device according to claim 19, wherein the at least one buffer reservoir comprises a buffer reservoir provided for each of the two vehicle brake circuits. 
     
     
       21. The brake pressure control device according to claim 19, wherein, for a road vehicle with front axle/rear axle brake circuit division, rear-axle drive, an anti-lock brake system and an acceleration skid regulation system, a feedback and open-loop control system is comprised of a return pump of the rear axle brake circuit constituting the auxiliary pressure source, a booster pump is arranged to supply the rear axle brake circuit return pump with brake fluid, a second booster pump is connected upstream of a return pump of the front axle brake circuit, and, a subsidiary hydraulic unit which includes the at least one buffer reservoir constituted by two buffer reservoirs and function control valves of the brake pressure control unit configured as 2/2-way solenoid valves for connecting the two buffer reservoirs to and shutting the buffer reservoirs off from the outlet pressure spaces of the brake unit.